The growth of solid state devices and particularly microelectronics has created a need for specialized types of cooling systems. These devices are very sensitive to temperature variations. Their operation depends on a semiconductor characteristic known as the band gap energy. This is the input energy required to move a charge carrier from the valence band to the conduction band and is manifested by an induced voltage or a change in the electrical impedance of the semiconductor device. Normally this energy is supplied by a photon, or other energy particle, the device is designed to detect. The bandgap is well defined at very low temperatures such as the boiling point of liquid nitrogen but becomes increasingly random at the higher temperatures found in most normal environments. A high performance device thus requires a constant source of cooling during its period of operation.
To stabilize such an electronic device at low temperatures it is common practice to seal it in a vacuum dewar. The device is placed against one inner wall of the dewar and the cold finger of a cooler is pressed against the outside of the same wall directly behind the device. A window for photons is formed by another part of the wall in close spaced proximity to the device. Such a dewar is shown in the U.S. Pat. No. 3,851,173 granted to Carol O. Taylor et al, Nov. 26, 1974.
To provide efficient and stable cooling the cold finger and the dewar must remain in intimate contact through the large temperature excursions encountered in normal operation. Since these two elements are generally made from different materials, i.e. glass and metal, an extensible end portion is usually added to the cold finger to maintain the required contact even through the expansion coefficients of these materials are not equal. These end portions usually consist of a coil spring covered by a sliding cap or extensible bellows. The cooling efficiency is substantially reduced by this arrangement and manufacture or maintenance of the assembly is made more difficult.